Temporal dynamics of Pinus tabulaeformis litter decomposition under nitrogen addition on the Loess Plateau of China

Litter decomposition in the early stage is determined by the release of easily decomposable substances, and that in the later stage is controlled by the contents of macromolecule compounds and microorganisms according to the two-stage model. However, the specific mechanism on how nitrogen (N) deposition changes litter decomposition on the basis of this model remains unknown. This study investigated the effects of multilevel N addition (control, low, medium, and high N amounts corresponding to 0, 3, 6, and 9 g N m(-2) y(-1), respectively) on the litter decomposition and nutrient release of Pinus tabulaeformis and the microbial community in the later stage on the Loess Plateau of China. Results were as follows. (1) N addition significantly increased the decomposition rate of P. tabulaeformis litter (P < 0.05) with the maximum value observed in the medium N treatment. (2) The release rates of soluble sugar, lignin, carbon (C), and N were significantly promoted by N addition with the best promotion effect found for medium N. Cellulose release was significantly inhibited by N addition, and medium N had the greatest inhibitory effect. (3) N addition had an insignificant effect on microbial community in later-stage decomposition but had significant influence on the relative abundances of Ascomycota, Zygomycota, and Davidiellaceae fungi. (4) Decomposition was controlled by the release of N, soluble sugar, and lignin in the early stage, and C release and three dominant fungal populations played important roles in the late stage. We conclude that the variations in N deposition, litter nutrient release and microbial community are important factors of decomposition and C flux in a forest ecosystem.